It has been known since the advent of magnetic recording tapes that their recording surfaces should be lubricated to permit sliding contact with recording heads and to inhibit adjacent convolutions of wound tape from sticking to each other after prolonged storage. The first lubricants were fatty acids and esters such as carnauba wax. These were either added to the dispersion of the magnetizable particles and binder resin or coated over the finished recording surface. The fatty acid/ester lubricants were considered to be satisfactory at ordinary ambient conditions but were not reliable at high temperatures and relative humidity, e.g., 40.degree. C and 80% relative humidity. Also, minor variations in the use of the lubricants, such as variations in coating weights, can destroy their utility.
Very early in the development of magnetic recording tape, it was suggested that silicones might provide better lubrication at high ambient temperatures and relative humidity. See U.S. Pat. No. 2,654,681 (Lueck). Because of their higher cost and questionable superiority, only about 25 percent of current flexible magnetic recording media employ silicone lubricants while about 70 percent have fatty acid/ester lubrication. A very small percentage of flexible magnetic recording media is lubricated with graphite, especially in endless-loop tape cartridges. See U.S. Pat. No. 2,804,401 (Cousino).
U.S. Pat. No. 3,490,946 (Wolff) suggests the use of fluorocarbon compounds as lubricants for flexible magnetic recording tapes, either applied as a surface layer or dispersed into the mixture of binder and magnetizable particles. U.S. Pat. No. 3,778,308 (Roller et al.) more specifically suggests perfluoroalkyl polyethers as lubricant coatings for magnetic recording media. U.S. Pat. No. 3,919,719 (Wright et al.) provides further information concerning the use of fluorinated polymers disclosed in U.S. Pat. No. 3,778,308.
U.S. Pat. No. 3,954,637 (Pardee et al.) prepares a surface lubricant for magnetic recording tape from a dispersion in trifluorotrichloroethane of (a) a copolymer of trifluoroethylene and vinyl chloride and (b) a telomer of tetrafluoroethylene. This is then filtered to remove undissolved polymeric solids to provide a solution from which the lubricant is applied, U.S. Pat. No. 4,096,079 (Pardee) concerns the lubrication of phonograph records without mentioning magnetic recording media. A phonograph record is coated with essentially the same solution as the coating solution of U.S. Pat. No. 3,954,637 except for omission of the chlorinated copolymer (a). The average molecular weight of the fraction of the telomer (b) after the filtering is between 400 and 900.
While it is believed that no magnetic recording tape now on the market employs a fluorinated lubricant, one manufacturer uses such a lubricant for the flexible magnetic recording disk of a diskette of the type shown in U.S. Pat. No. 3,668,658 (Flores et al.).